Twenty-three athletes from five sports and six National Olympic Committees failed doping tests in a reanalysis of samples from the 2012 London Olympics, the International Olympic Committee (IOC) said Friday.
Retests were carried out on 265 selected doping A samples based on intelligence-gathering that began in August 2015, the IOC said Friday.
The reanalysis programme is continuing and more results could follow in the coming weeks.
The latest unnamed cases come just over a week after the IOC said 31 athletes tested positive in retesting of 454 samples from the 2008 Beijing Games. A further sample later showed abnormal parameters which the IOC is also following up.
The B samples of all the retested samples are yet to be analysed.
The IOC said all athletes found to have doped would be banned from competing at the 2016 Games in Rio in August.
IOC president Thomas Bach said: "These reanalyses show, once again, our determination in the fight against doping.
"We want to keep the dopers away from the Olympic Games in Rio de Janeiro.
"This is why we are acting swiftly now. I have already appointed a disciplinary commission, which has the full power to take all the decisions on behalf of the IOC."
The retesting of samples from the Beijing and London Games is using the latest scientific methods and has mainly focused on athletes who could potentially participate at the 2016 Games.
The athletes, national Olympic committees and international federations are being informed before proceedings begin against the athletes concerned.
The positive Beijing doping retests affect 12 national Olympic committees and six sports.
According to Russia's Tass news agency this week, Olympic high jump champion Anna Chicherova of Russia is among the athletes who tested positive from the Beijing samples.
The state agency also said that 14 of athletes were Russians, citing a source from the nation's Olympic committee, and that most of them were from athletics.
Chicherova was a gold medallist at the London Games after winning bronze at the Beijing Games.
Her coach Yevgeny Zagorulko was quoted by Tass as saying: "Three days ago, Anna received a notice that her doping sample from the Beijing Olympic tested positive after a recheck and she called me."
Russia has been rocked by doping allegations, with its athletics federation suspended and in danger of missing Rio. A final decision is to be made by mid-July.
In addition, the former head of the Moscow anti-doping lab, Grigory Rodchenkov, told the New York Times recently that 15 Russian medallists from the Sochi 2014 Winter Olympics were doped.
Rodchenkov said he helped provide performance-enhancing drugs to athletes and switch out drug-tainted test samples with clean ones.
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